I just built a great PC for my home entertainment unit.  It is based
on the Shuttle AMS Bare Bone GBox Model CF-968 for Intel Processors.

http://www.newegg.com/app/Showimage.asp?image=56-101-603-02.jpg/56-101-603-03.JPG/56-101-603-04.jpg/56-101-603-05.JPG/56-101-603-06.jpg/56-101-603-07.jpg/56-101-603-08.jpg

Now I want to dump the windows xp i put on there for xp media edition.
Can I buy it separately and install it.  If it is not purchasable, can
I take the copy that came with my HP Media Center PC and install it?

I heard you have to have a compatible remote control and a compatible
video capture card. Where can I get these?

I have been interested in this, as well.  It would be nice to take
advantage of the "living room" interface for reading the screen from
across the room.

Unfortunately, the software is only available to OEMs who build the
machines.  The product manager says that they did this to ensure that
purchasers had compatible hardware.  However, the product manager
indicates that the next version may be available without hardware
purchase, though no timeframe was suggested.

To the best of my knowledge, the video card and remote are not widely
available.  One thought I pondered was ordering "replacement" parts
from an OEM.

Since I am not providing a source for you to acquire the hardware, I
wanted to leave this as a comment, instead of an answer.  For further
information about the Media Center edition, you may enjoy reading the
Microsoft discussion group available from Microsoft's Windows Media
Center home page:
http://www.microsoft.com/windowsxp/mediacenter/